Optical surface generating apparatus

ABSTRACT

A surface generating system wherein a polishing electrode comprising a continuous stream of electrolyte is used to selectively polish an optical blank. During movement over the blank&#39;&#39;s surface, the electrode is selectively energized by a sensor element synchronously moving over a guide retaining information regarding contour errors on the surface blank.

O Unlted States Patent 1 1 3,669,867 Adachl 145] June 13, 1972 [54]OPTICAL SURFACE GENERATING 3,301,776 1/1967 Hughes...... ..204 143APPARATUS 3,463,720 8/1969 Wilkinson ..204/143 2,848,410 8/1968Kauth-Winterfeld et al.. 204/ 140 5 lnvemorl 1W9 Adachl, Lexmgtom Mass.3,293,162 12/1966 Sullivan ..204 224 73 Assigneez ck Corporation,Lexington, Mass. 3,338,807 8/1967 Clifford ..204/l43 3,466,235 9/1969Williams.... .....204/l43 1 Flledi April 15, 1968 3,474,013 /1969 lnove..204 143 [2!] Appl' 72147l Primary Examiner-J. H. Mack AssistantExaminer-Regan J. Fay [52] US. Cl ..204/224, 51/165, 51/284,Att0rneyHomer 0. Blair, Robert L. Nathans, Lester 5.

90/135, 90/137, 156/345, 204/140.5, 204/212, Grodberg and John E. Toupal219/69 E [51] Int. Cl. ..B23p l/02, C23b 5/76, E05d /22 [57] ABSTRACT[58] Field ofSearch ..204/224, 212, 140.5; 51/165,

51/143 284; /117 13.4 119 A surface generatmg system wherem a pollshmgelectrode compnsmg a contmuous stream of electrolyte is used to selec-[56] References Cited tively polish an optical blank. During movementover the blanks surface, the electrode is selectively energized by asen- UNITED STATES PATENTS sor element synchronously moving over a guideretaining information regarding contour errors on the surface blank.2,814,237 11/1957 Sehmid ..90/13.4 3,23 8,675 3/1966 Abbott et al ..5 H14 Claims, 9 Drawing Figures PATENTEDJUMB m2 3,669,867

saw 1 BF 5 Iaweaatom Iwao P. JIM,

attorney PA'TENTEDJUII 13 m2 SHEEI 26$ 5 P'A'TE'N'TEnJum 1922 3,669,867sum w s l 7 86 i 4/ as l 39 I VOLTAGE 94 I SOURCE l I l OPTICAL SURFACEGENERATING APPARATUS BACKGROUND OF THE INVENTION This invention relatesgenerally to a method and apparatus for generating optical surfaces Moreparticularly, the invention relates to method and apparatus forcorrecting asymmetrical imperfections in the surfaces of optical blanks.

According to known methods, optical surfaces are ground and polished byutilizing completely empirically developed techniques. The practice ofoptical surface generation in accordance with these techniques'suffersfrom a number of significant disadvantages including requirements forlengthy processing and for highly skilled technicians. Furthermore,since such empirically developed techniques are designed to producesymmetrical alteration of optical surfaces, they are generallyinappropriate for eliminating asymmetrical deviations from a desiredsurface contour. This latter deficiency is particularly troublesome withregard to relatively large optical surfaces of, for example, 50-inchdiameter and larger in which rotational asymmetries and randomirregularities are more prominent than in smaller surfaces. Also knownare so called template grinding systems wherein a polishing tool iscontrolled by a guide having a surface configuration conforming to thesurface conto'urdesired for the optical blank. The surface qualityproduced with such systems is limited obviously by both the precision ofthe mechanical equipment used and the exactness of the guide itself.Furthermore, template systems are similarly unsuitable for correctingasymmetrical surface errors. Thus, a general need exists for improvedoptical surface generation systems and especially for generation systemscapable of producing asymmetrical surface changes.

The object of this invention, therefore, is to provide an improvedoptical surface generating system that can be selectively controlled toeliminate asymmetrical imperfections in an optical surface.

CHARACTERIZATION OF THE INVENTION The invention is characterized by theprovision of an optical surface generating system including a surfacemodifying means movable along the work surface of an optical blank in apath including in sequence a plurality of discrete areas thereon, aguide device retaining indicia regarding the initial contour of the worksurface, a sensor element movable relative to the guide device, asynchronizing mechanism for synchronizing the movements of the sensorelement and the surface modifying means, and a controller for alteringthe relative elevational changes produced in the discrete areas by thesurface modifying means in response to the position of the sensorelement with respect to the guide device. In this system, the use of acontour information retaining guide device to control movement of asurface modifying means permits selective modification of the opticalwork surface. Therefore, asymmetrical irregularities can be eliminatedin a precise, programmed manner. Furthermore, the required equipmentcosts of the system are relatively small compared to those of morecomplex systems.

One feature of this invention is the provision of an optical surfacegenerating system of the above type wherein two components of relativemovement are produced between both the work surface and the surfacemodifying means and between the guide device and the sensor element. Ina preferred embodiment, the two dimensional relative movement isprovided by synchronously rotating the optical blank and guide deviceand by synchronously reciprocating the surface modifying means andsensor element. in this arrangement, the desired two dimensionalrelative movement is obtained with relatively simple and inexpensiveequipment.

Another feature of this invention is the provision of an optical surfacegenerating system of the above type wherein the guide device is acontour map of the work surface, the sensor element moves over thesurface of the contour map and the surface modifying means responds tothe position of the sensor element with respect to the contour lines onthe contour map. Specially prepared contour maps are highly suitable foruse as guides to control selective modification of the optical surface.

Another feature of this invention is the provision of an optical surfacegenerating system of the above type wherein surface portions betweencertain contour lines on the contour map are sensitized and thecontroller either activates or deactivates surface modifying action ofthe surface modifying means in response to movement of the sensorelement over the sensitized surface portions. With this embodiment, ahigh degree of surface polishing selectiveness is provided with arelatively simple on-off control system.

Another feature of this invention is the provision of an optical surfacegenerating system of the above featured type wherein the sensor elementcomprises spaced electrodes movable on the surface of the contour mapand the sensitized map surface portions are electrically conductive.Movement of the spaced electrodes onto a sensitized surface portioncompletes an electrical circuit which either activates or de-activatesthe surface modifying means.

Another feature of this invention is the provision of an optical surfacegenerating system of the above featured types wherein the surfacemodifying means comprises a source of surface polishing electricalenergy suitable for removing material from the work surface of theoptical blank. Because of the ease with which they can be controlled,electrical energy surface polishing mechanisms are particularly wellsuited for use in this application.

Another feature of this invention is the provision of an optical surfacegenerating system of the above type including a position compensatorwhich modifies the effectiveness of the surface modifying means independence upon its radial position over the work surface. The variationin surface modification effectiveness compensates for the differenttangential speeds of radially spaced discrete areas on the rotating worksurface.

The invention is characterized further by the provision of an opticalsurface generating system comprising an anode electrode adapted forelectrical connection with the conductive work surface of an opticalblank, a cathode electrode, a blank support adapted to support theoptical blank with its work surface spaced adjacent the cathodeelectrode, drive means for producing relative transverse movementbetween the cathode electrode and the work surface, and an electrolytemaintenance means for maintaining a body of electrolyte between thecathode electrode and the work surface. According to this system,programmed electrolytic polishing of an optical work surface is producedby selectively moving the cathode electrode relative to the worksurface;

Another feature of the invention is the provision of an optical surfacegenerating system of the above type wherein the electrolyte maintenancemeans comprises a fluid supply unit which supplies a stream ofelectrolytic fluid between the cathode electrode and the work surface.The continuously supplied stream of electrolyte functions as anelectrode as well as ion exchange media and limits the surface regionbeing polished to that area directly contacted by the electrolytecolumn. In addition, the agitation produced by the continuouslycirculated electrolyte reduces the formation of reactionary products onthe work surface thereby improving the quality of the finished surface.

Another feature of the invention is the provision of an opticalgenerating system of the above featured type wherein the fluid supplyunit includes a fluid supply tube mounted for movement with the cathodeelectrode and adapted to circulate electrolyte from a supply reservoirover the cathode electrode and onto the work surface of the opticalblank. Preferably, the electrolyte reservoir is a vessel disposed tocollect electrolyte discharged onto the optical blanks work surfacethereby providing a closed fluid circulation system.

The invention is characterized further by the provision of a method forgenerating optical surfaces comprising the steps of providing anelectrical connection between an anode electrode and a conductive worksurface of an optical blank, positioning a cathode electrode adjacentthe work surface, providing a body of electrolyte between the cathodeelectrode and the work surface, establishing an electrical potentialbetween the anode and cathode electrodes, and moving the cathodeelectrode in a predetermined transverse path relative to the worksurface. The predetermined path is selected so as to produceelectrolytic polishing of discrete predetermined regions on the worksurface of the optical blank.

Another feature of this invention is the provision of a method of theabove type wherein the body of electrolyte comprises a stream ofelectrolytic fluid continuously circulating between the cathodeelectrode and work surface. According to this method, the agitationproduced by the streaming electrolyte prevents the formation ofreactionary products on the optical blanks work surface and on thesurface of the cathode electrode.

Another feature of the invention is the provision of a method of theabove featured type wherein the work surface is created by depositing afilm of electrically conductive material on an optical blank formed ofan electrically non-conductive material. The deposited film ofelectrically conductive material permits the exercise of electrolyticpolishing on a blank formed of a conventional optical material such asglass or plastic.

Another feature of this invention is the provision of a method of theabove featured type wherein the conductive material deposited upon theoptical blank comprises chromium or rhodium. Because of both theirphysical and optical properties, chromium and rhodium are uniquelysuited for use as a surface coating material in this application.

These and other characteristics and features of the present inventionwill become more apparent upon a perusal of the following specificationtaken in conjunction with the accompanying drawings wherein:

- FIG. 1 is a schematic plan view of a preferred embodiment of theinvention;.

FIG. 2 is a cross-sectional view taken along the lines 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along the lines 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken along the lines 4-4 of FIG. 1;

FIG. 5 is a circuit diagram illustrating a control system for thesurface generating embodiment shown in FIG. 1;

FIG. 6 is a plan view of a contour map for use with the in ventionembodiment shown in FIG. 1; and

FIGS. 7-9 are plan views of other contour maps suitable for use with theinvention embodiment shown in FIG. 1.

Referring now to FIG. 1 there is shown the optical surface polishingsystem 11 including the surface modifying assembly 12 mounted above theoptical blank 13. Supporting the assembly 12 is one end of the arm 14having an opposite end supporting the sensor element 15. A guidemechanism including the contour map 16 and supporting turntable 17 aredisposed below the sensor element 15.

The support bar 18 is connected between the mid-portion of the arm 14and the drive assembly 21. Included in the drive assembly 21 is thehousing 22 which supports the ball slide 23 and the worm shaft 24.Mounted on the housing 22 is the power supply 26 and associated motor 25operatively coupled to the worm shaft 24. The electrical leads 27connect the contact switches 28 and 29 with the power supply 26.

As shown in FIG. 2, the support bar 18 is secured to the transport table31 by the mounting block 32. Supporting one end of the transport table31 is the slide bearing 33 adapted for longitudinal movement along theball slide 23. The opposite end of the transport table 31 is supportedby the bracket 34 that terminates with rollers 35 that are retained byand adapted for movement within the groove 36 in the side wall of thehousing 32. Internal threads on the collar 37 engage the worm drive 24so as to produce movement of the transport table 31 in response torotation thereof.

Secured to, for movement with the transport table 31 is the angle arm 38having an end attached to the adjustment rod 39 of the voltage dividingpotentiometer 41. The electrical cable 42 connects the potentiometer 41to the power supply 43 which supplies electrical energy to the surfacepolishing assembly 12 through the electrical cable 44. Also connected tothe power supply 43 by the electrical cable 45 is the sensor element 15.

The fluid supply unit 47 includes a supply tank and conventional fluidpump that circulates fluid through the supply tubes 48 and 49 fordischarge by the polishing assembly 12. Fluid discharged by the assembly12 contacts the optical blank 13 and is accumulated in the collectionvessel 51. A closed system is provided by the return tube 52 thatconveys fluid back to the supply unit 47 from the collection vessel 51.

As shown more clearly in FIG. 3, the optical blank 13 is mounted on thesupport plate 53 within the collection vessel 51. Fixed for rotationwith the plate 53 is the shaft 54 that extends through the fluid seal 55in the bottom wall of the collection vessel 51. The optical blank 13comprises the electrically non-conductive substrate 56 composed, forexample, of optical glass or plastic and the deposited layer 57 ofelectrically conductive material. Rotation of the shaft 54 and plate 53is produced by the belt 61 which is driven by the wheel 62 of the drivemotor 63, as shown in FIG. 1.

Referring again to FIG. 3, the surface polishing assembly 12 includesthe screen anode electrode 71 disposed within the rigid terminal portion70 of the fluid supply tube 49 and the screen cathode electrode 72disposed within the rigid terminal portion 69 of fluid supply tube 48.The anode and cathode electrodes 71 and 72 and the fluid supply tubes 48and 49 are supported by the mounting plate 73 secured to one end of thearm member 14. Electrical energy is supplied to the anode and cathodeelectrodes 71 and 72 from the power supply 43 by leads included in theelectrical cable 44.

' As shown in FIG. 4, the sensor element 15 comprises the spaced apartbrush electrodes 75 and 76 mounted for movement along the surface of thecontour map 16. The electrodes 75 and 76 are connected to the powersupply 43 by the electrical leads 45. Supporting the turntable 17 is theshaft 77 which also is driven by the drive wheel 62 (FIG. 1) via belt78. Thus, the contour map 16 and the optical blank 13 are synchronouslydriven at equal rotational speeds by the drive motor 63.

The control circuit for the surface modification system 11 isillustrated in FIG. 5. As shown, the power supply 43 includes the dcvoltage source 81 that excites a dc potential between output terminals82 and 83. Also included in the power supply 43 is the relay 84 havingthe normally open switch contact 85 connected between the voltage source81 and positive output terminal 82. The winding 86 of the relay 84 isconnected in series with the brush contacts 75 and 76 directly acrossthe dc voltage source 81. Coupled across the output terminals 82 and 83is the rectilinear potentiometer 41, the output of which is connected tothe anode and cathode electrodes 71 and 72 of the surface polishingassembly 12.

During operation of the system 11, the fluid supply unit 47 is actuatedto produce a continuous flow of an electrolyte through the fluid supplytubes 48 and 49. Suitable electrolytes include, for example, nickeloussulphate solutions or potassium nitrate solutions. The continuouslypumped electrolyte flows over the anode and cathode electrodes 71 and 72and is discharged as a stream onto the conductive coating 57 of theoptical blank 13. After excitation of the electrodes 71 and 72 by thepower supply 43, the discharging streams of electrolyte function both aselectrodes and as ion exchange media. Accordingly, electrolyticpolishing action occurs on that area of the coating 57 directly belowthe cathode electrode 72.

The disassociation of ions from the surface coating 57 produced by theelectrolytic action results in a gradual displacement of materialtherefrom. The rate and type of material removal effected are influencedby various factors including the power output of the power supply 43,the kind of electrolyte used, the spacings of the electrodes 71 and 72from the surface 57, etc. In a preferred embodiment, the electrodes 71and 72 are excited by one microsecond pulses that produce momentarydensities of 5-15 amperes per square foot. This output establishes asatisfactory rate of surface polishing without completely dissolving thefilm layer 57. The pulsed signal can be established in the power supply43, for example, by a conventional current interrupter such as avibrator.

The agitation produced by the continuously circulating electrolyteprevents formation of the reaction products normally associated with anelectrolytic process. For this reason, the surface of film coating 57 ismaintained clean thereby both insuring a constant rate of materialremoval and enhancing the surface quality of the finished product;Furthermore, since surface polishing occurs only in the particular areadirectly below the electrolyte column emanating from the cathodeelectrode 72, the surface 57 can be selectively polished by appropriatemovement of the assembly 12 as described more fully below. Thus, the useof a continuously circulating body of electrolyte permits selectivepolishing of discrete areas and produces high quality finished surfaces.

Relative movement between the surface modifying as sembly l2 and theoptical blank 13 is introduced by energizing both the drive motor 63 andthe drive assembly 21. Rotation of support plate 53 produces acircumferential component of relative movement between the surface 57and the cathode electrode 72. Simultaneously, rotation of the turntable17 produces a synchronized circumferential component of relativemovement between the contour map 16 and the sensor element 15. Asdescribed further below, this latter movement controls the excitation ofthe electrodes 71 and 72 and thereby the surface modification producedby the polishing assembly 12. Additional, radially directed componentsof relative movement between the cathode electrode 72 and the opticalsurface 57 and between the sensor element 15 and the contour map guide16 are produced by reciprocal movement of the transport table 31 asfollows. Responsive to energization of the motor 25, the rotating worm24 drives the operatively engaged transport table 31 in a reciprocatingmovement between the contact switches 28 and 29. Upon each contactbetween the table 31 and either of the switch contact 28 and 29, themotor power supply 26 is activated in a conventional manner to reversethe rotational direction of the drive motor 25. Thus, the transporttable 31 is driven in a reciprocating motion between the switch contacts28 and 29. Consequently, the integrally connected cathode electrode 72and the sensor element 15 are synchronously driven in reciprocatingradially disposed paths above, respectively, the optical surface 57 andthe contour map 16. Because of the two components of relative movement,the cathode electrode 72 and the sensor element 15 pass over all surfaceportions of, respectively, the optical surface 57 and the contour map16. Furthermore, because both the rotational movements of the opticalblank 13 and the contour map 16 and the reciprocating movements of thesensor element 16 and the cathode electrode 72 are in synchronism, therelative position of the sensor element 15 above the contour map 16 isalways directly related to the relative position of the cathodeelectrode above the optical surface 57.

During its movement relative to the optical surface 57, the sensorelement 15 periodically passes over sensitized contour map regions 91.According to a preferred method, a layer of electrically conductivecopper is applied to sensitize the regions 91. Thus, when the brushelectrodes 75 and 76 of the sensor element 15 contact a sensitizedregion 91, a conductive path is established through the relay winding 86as illustrated in FIG. 5. This closes switch contacts 85 and results inthe application of source voltage across the anode and cathodeelectrodes 71 and 72. Consequently, the surface modifying assembly 12 isactivated to produce surface polishing. Conversely, when the brushelectrodes 75 and 76 are in contact with non-sensitized regions of thecontour map 16, the relay winding 86 is deenergized, switch contacts 85remain open and the surface polishing assembly 12 is de-activated. Itwill be obvious, therefore, that selective polishing of the opticalsurface 57 can be achieved by sensitizing predetermined portions of thecontour map 16.

According to a preferred method embodiment of the invention, the surface57 of the optical blank 13 is measured with suitable test apparatus. Themeasurements can be made mechanically, for example, with dial indicatorsor traversing probes. However, the measurements preferably are made inthe conventional manner by an interferometer which produces aninterference picture indicating the contour characteristics of thesurface 57. The surface information provided by the interference picturethen is used to produce the typical contour map 16. As shown in FIG. 6,the contour map 16 possesses contour lines each representing points onthe surface 57 of a constant elevational error with respect to a desiredreference. For example, the lines 92 represent points on the surface 57lying 20 elevational units above a desired reference, lines 93 representpoints lying l5 elevational units above the desired reference, lines 94represent points lying l0 elevational units above the desired reference,and lines 95 represent points lying 5 elevational units above thedesired reference. Accordingly, it will be obvious that generation ofthe surface desired on the optical blank 13 requires removal of largervolumes of material from those portions of the surface 57 represented bycontour lines 92 than by those portions represented by contour lines 93.Similarly, a larger volume of material must be removed from thoseportions of the surface 57 represented by the contour lines 93 than fromthose portions represented by the contour lines 94, etc. However, sincethe contour lines 92-95 and, therefore, the surface errors representedthereby are asymmetrical, an irregular pattern of material removal isrequired to produce the desired surface contour. It is precisely thistype of asymmetrical surface correction that cannot be readilyaccomplished by conventional polishing systems but that is producedaccording to the present invention in a highly precise and predictablemanner as described below.

First, the map regions 91 defined by the highest contour error lines 92and containing no other contour lines are covered with an electricallyconductive coating, of, for example, copper. Naturally, the regions 91represent areas on the surface 57 having the greatest elevationalerrors. The map 16 then is placed on the turntable 17 and accuratelyaligned thereon with respect to the optical blank 13. The alignment issuch that the sensor element 15 lies directly above that particular areaof the contour map 16 representing the corresponding area of the blanksurface 57 above which the cathode electrode 72 is positioned. Since, asnoted above, the various components move in synchronism, it will beobvious that once established this relationship will persist. Thus, thesensor element 15 and cathode electrode 72 will be disposed continuouslyabove corresponding areas of, respectively, the contour map 16 and theoptical surface 57. Next, the drive motor 63 is energized to producerotation of the blank support plate 53 and the turntable 17, and themotor 25 is energized to produce reciprocating movement of the sensorelement 15 and the surface polishing assembly 12.

During each movement of the sensor element 15, over the conductivelycoated regions 91, voltage is applied between the anode and cathodeelectrodes 71 and 72 as described above. Consequently, electrolyticpolishing occurs invthose areas of the optical surface 57 represented bythe contour map regions 91. However, when the sensor element 15 is aboveall portions of the contour map 16 except for the sensitized regions 91,the anode and cathode electrodes 71 and 72 are de-activated so as tointerrupt the surface polishing process. This phase of the polishingoperation is continued for a given time period of sufficient length toeffect removal of predetermined material volumes from those areas of theoptical surface 57 represented by the contour map regions 91. Thepredetermined volumes of surface material correspond to approxi mately 5of the elevational units represented by the contour lines 92-95. Thus,the contour errors of the surface areas denoted by the map regions 92are reduced to values less than 20 elevational units but greater than 15elevational units.

After completing the first phase of the polishing process, the contourmap 16 is removed from the turntable l7 and replaced by the contour map101 illustrated in FIG. 7. The map 101 is identical to map 16 exceptthat the sensitized regions 91 of map 16 have been supplanted by thesensitized region 102 also formed, for example, by the application of anelectrically conductive layer of copper. The sensitized region 102 isdefined between contour lines 93'and contains only contour lines 92.Thus, the region 102 represents that area of the optical surface 57having contour errors of greater than 15 elevational units. Again, thecontour map 101 is accurately aligned with respect to the optical blank13 and the above described polishing process resumed. This secondsurface polishing phase continues for another given period of sufficientlength to effect removal of a predetermined volume of material. Duringthis period the relative elevation of the surface 57 represented byregion 102 is reduced by approximate- 1y 5 elevational units. Thus, theprescribed area possesses a contour error of greater than but less thanelevational units.

For the next phase of the process, contour map 101 is replaced bycontour map 106 (FIG. 8). Map 106 has a sensitized region 107 defined bythat map area lying between contour lines 94 and containing contourlines 92 and 93. Upon completion of this phase in the manner describedabove, the area of the optical surface 57 represented by the sensitizedregion 107 exhibits relative contour error values of greater than 5 butless than 10 elevational units. 1

During the final phase of the process, the map 105 is replaced by thecontour map 108 having a sensitized region 109 lying between the contourlines 95 and containing contour lines 92, 93 and 94. After completion ofthis final phase in the manner described above, the entire opticalsurface 57 possesses relative contour error values of less than 5 butgreater than 0 elevational units. Thus, the maximum relative contourerror of greater than elevational units that existed initially isreduced to a maximum of less than 5 elevational units. Furthermore, thereduction in maximum relative surface error is obtained in a highlyefficient and predictable manner with relatively simple and inexpensiveequipment.

Referring again to FIG. 1, it will be noted that during reciprocalmovement of the transport table 31, the potentiometer 41 is adjusted bymovement of the rod 39. The variable settings of the potentiometer 41produce corresponding variations in the current supplied to the anodeand cathode electrodes 71 and 72 as indicated by the circuit diagram ofFIG. 5. Preferably, a relationship is established between thepotentiometer 41 and the drive assembly 21 such that the potentiometer41 provides a variable output current that increases linearly independence upon the radial distance of the cathode electrode 72 from thecenter of the optical blank 13. Thus, a minimum value of polishingcurrent is applied when the cathode electrode 72 is over the center ofthe optical blank 13 and a maximum value is applied when the cathodeelectrode 72 is over the outer edge thereof. The variable rates ofmaterial removal produced by the changing current tend to compensate forthe different tangential speeds of radially spaced discrete areas on thesurface 57 of the rotating blank 13. For example, although disposedbeneath the cathode electrode 72 for shorter periods of time than areinner portions of surface 57, the outer portions thereof are subject tocompensating higher current densities. For this reason the actual ratesof surface polishing produced in all radial areas of the surface .57 aresomewhat equalized. It will be appreciated that in certain applicationsother more sophisticated relationships between applied current andradial position may be found desirable.

Although useful in other surface generation applications, the presentinvention is particularly well suited for correcting the surfaces ofoptical glass reflectors to an accuracy of an order of a few hundredthsof a wavelength (A). This is the application illustrated in FIG. 3wherein the glass substrate 56 is adapted for electrical polishingtechniques by the deposition of the metal coating 57. In a preferredembodiment of the invention, the surface of the glass blank 56 first isground and polished and then coated with a metal film 57 having athickness corresponding to the maximum surface error still existing onthe blanks surface. After deposition by, for example, vacuum techniquesselective portions of the metal film 57 are removed according to theabove described electropolishing process so as to correct irregularitiesexisting on the initial surface of the glass blank 56. Upon completionof the electropolishing process, the corrected metal surface 57 can beover-coated with a suitable material such as aluminum to improvereflectivity. It has been found highly desirable that the original glassblank 56 be initially polished to the extent required for elimination ofsurface errors greater than k A. This is because the removal of metalfrom the surface 57 in amounts corresponding to greater than a A isaccompanied by a degradation of surface quality. Apparently, the qualityreduction results from a surface cloudiness caused by the oxidation thataccompanies the electrolytic polishing action.

It has been found that chromium is an uniquely suitable metal for use informing the conductive layer 57. In addition to a highly desirablehardness, chromium exhibits an adhesion characteristic that enchancesits ability to be deposited and retained on the surface of the glassblank 13. Furthermore, chromium produces a highly specular surface withsignificantly less scattering than do most other metals. It is believedthat the high surface quality results from the fact that during theelectropolishing process chromium ions are removed individually ratherthan in clusters. Another vary suitable metal that closely resembleschromium in desirable characteristics is rhodium.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. For example, although thedescribed method utilizing a continuously circulating stream ofelectrolyte produces particularly desirable results, it will beappreciated that the invention could be practiced also in a systemwherein the electrodes 71 and 72 and the optical blank 13 are fullysubmerged in an electrolytic bath. Also, control systems other thanthose shown and described can be used to control movement of the surfacemodifying assembly 12. Other suitable control methods and systems aredisclosed, for example, in the commonly assigned, copending US.Application Ser. No. 719,657 now US. Pat. No. 3,587,195 of Ronald Aspdenentitled Optical Surface Generating Method and Apparatus," filed Apr. 8,1968.

Similarly, the described control system could be utilized to controlpredetermined movements of other surface modifying mechanisms including,for example, ion beams, metal vapor streams, optical laps, etc. It is tobe understood, therefore, that within the scope of the appended claimsthe invention can be practiced otherwise than as specifically described.

What is claimed is:

1. Optical surface generating apparatus for generating a desired contouron the surface of an optical blank comprising blank support means forsupporting an optical blank, surface modifying means for alteringrelative elevations on the work surface of an optical blank supported bysaid blank support means, drive means for moving said surface modifyingmeans along the work surface in a path including in sequence a pluralityof discrete areas thereon, guide-means for retaining informationregarding the initial contour of the work surface and elevational errorsbetween the initial contour of said work surface and said desiredcontour, sensor means movable relative to said guide means by said drivemeans for sensing said information, synchronizing means forsynchronizing movements of said sensor means and said surface modifyingmeans, and control means for controlling the relative elevationalchanges produced in said discrete areas by said surface modifying meansin response to the position of said sensor means with respect to saidguide means.

2. Optical surface generating apparatus according to claim 1 whereinsaid drive means is adapted to produce first and second components ofrelative movement between said surface modifying means and the worksurface and first and second components of relative movement between thesensor means and guide means.

3. Optical surface generating apparatus according to claim 2 whereinsaid drive means produces said first components of relative movement bysynchronously moving said guide and the work surface and produces saidsecond components of relative movement by synchronously moving saidsurface modifying means and said sensor means.

4. Optical surface generating apparatus according to claim 3 whereinsaid sensor means and surface modifying means are joined by connectormeans so as to be moved in unison by said drive means.

5. Optical surface generating apparatus according to claim 4 whereinsaid drive means is adapted to produce rotation of the optical blank andguide means and reciprocating movement of said surface modifying meansand said sensor means.

6. Optical surface generating apparatus according to claim 5 includingrotary movement compensation means adapted to provide said surfacemodifying means with a surface modification rate proportional to itsradial position with respect to the work surface.

7. Optical surface generating apparatus according to claim 1 whereinsaid guide means comprises a contour map of the work surface, said drivemeans is adapted to produce transverse movement of said sensor meansover the surface of said contour map, and said control means controlssaid surface modifying means in response to the position of said sensormeans with respect to the contour lines on said contour map.

8. Optical surface generating apparatus according to claim 7 whereinsaid control means is adapted to activate and de-activate surfacemodifying action of said surface modifying means in response to theposition of said sensor means with respect to said contour lines.

9. Optical surface generating apparatus according to claim 8 whereinsurface portions between certain contour lines on said contour map aresensitized, and said control means is adapted to produce either saidactivating or said de-activating action in response to passage of saidsensor means over said sensitized surface portions.

10. Optical surface generating apparatus according to claim 9 whereinsaid sensor means comprises spaced electrodes adapted for movement onthe surface of said contour map, and said sensitized surface portionsare electrically conduc tive.

11. Optical surface generating apparatus for generating a desiredcontour on the surface of an optical blank comprising blank supportmeans for supporting an optical blank, surface modifying means foraltering relative elevations on the work surface of an optical blanksupported by said blank support means, drive means for moving saidsurface modifying means along the work surface in a predetermined path,a plurality of guides for retaining information regarding the initialcontour of said work surface, each of said plurality of guides retaininginformation regarding elevational errors in one of a plurality ofdiscrete areas on said work surface, sensor means movable relative tosaid guides for sequentially sensing the contour information on each ofsaid plurality of guides, synchronizing means for synchronizingmovements of said sensor means and said surface modifying means, andcontrol means for controlling the relative elevational changes producedin each of said discrete areas by said surface modifying means inresponse to the position of said sensor means with respect to each ofsaid plurality of guides.

12. Optical surface generating apparatus according to claim 1 1 whereineach of said guides retains information regarding a predetermined rangeof elevational error relative to a reference elevation, and wherein saidsensor means sequentially moves relative to said plurality of guidesfrom the guide retainintg information of largest elevational errorrelative to said re erence to the guide retaining information of leastelevational error relative to said reference.

13. Optical surface generating apparatus according to claim 12 whereinsaid guides comprise a plurality of contour maps, the contour lines ofeach map representing points of constant elevational error relative tosaid reference.

14. Optical surface generating apparatus according to claim 13 whereineach of said plurality of contour maps have the areas between differentcontour lines sensitized for the production of activating ordeactivating surface modifying action by said surface modifying means inresponse to passage of said sensor means over said sensitized portions.

1. Optical surface generating apparatus for generating a desired contouron the surface of an optical blank comprising blank support means forsupporting an optical blank, surface modifying means for alteringrelative elevations on the work surface of an optical blank supported bysaid blank support means, drive means for moving said surface modifyingmeans along the work surface in a path including in sequence a pluralityof discrete areas thereon, guide means for retaining informationregarding the initial contour of the work surface and elevational errorsbetween the initial contour of said work surface and said desiredcontour, sensor means movable relative to said guide means by said drivemeans for sensing said information, synchronizing means forsynchronizing movements of said sensor means and said surface modifyingmeans, and control means for controlling the relative elevationalchanges produced in said discrete areas by said surface modifying meansin response to the position of said sensor means with respect to saidguide means.
 2. Optical surface generating apparatus according to claim1 wherein said drive means is adapted to produce first and secondcomponents of relative movement between said surface modifying means andthe work surface and first and second components of relative movementbetween the sensor means and guide means.
 3. Optical surface generatingapparatus according to claim 2 wherein said drive means produces saidfirst components of relative movement by synchronously moving said guideand the work surface and produces said second components of relativemovement by synchronously moving said surface modifying means and saidsensor means.
 4. Optical surface generating apparatus according to claim3 wherein said sensor means and surface modifying means are joined byconnector means so as to be moved in unison by said drivE means. 5.Optical surface generating apparatus according to claim 4 wherein saiddrive means is adapted to produce rotation of the optical blank andguide means and reciprocating movement of said surface modifying meansand said sensor means.
 6. Optical surface generating apparatus accordingto claim 5 including rotary movement compensation means adapted toprovide said surface modifying means with a surface modification rateproportional to its radial position with respect to the work surface. 7.Optical surface generating apparatus according to claim 1 wherein saidguide means comprises a contour map of the work surface, said drivemeans is adapted to produce transverse movement of said sensor meansover the surface of said contour map, and said control means controlssaid surface modifying means in response to the position of said sensormeans with respect to the contour lines on said contour map.
 8. Opticalsurface generating apparatus according to claim 7 wherein said controlmeans is adapted to activate and de-activate surface modifying action ofsaid surface modifying means in response to the position of said sensormeans with respect to said contour lines.
 9. Optical surface generatingapparatus according to claim 8 wherein surface portions between certaincontour lines on said contour map are sensitized, and said control meansis adapted to produce either said activating or said de-activatingaction in response to passage of said sensor means over said sensitizedsurface portions.
 10. Optical surface generating apparatus according toclaim 9 wherein said sensor means comprises spaced electrodes adaptedfor movement on the surface of said contour map, and said sensitizedsurface portions are electrically conductive.
 11. Optical surfacegenerating apparatus for generating a desired contour on the surface ofan optical blank comprising blank support means for supporting anoptical blank, surface modifying means for altering relative elevationson the work surface of an optical blank supported by said blank supportmeans, drive means for moving said surface modifying means along thework surface in a predetermined path, a plurality of guides forretaining information regarding the initial contour of said worksurface, each of said plurality of guides retaining informationregarding elevational errors in one of a plurality of discrete areas onsaid work surface, sensor means movable relative to said guides forsequentially sensing the contour information on each of said pluralityof guides, synchronizing means for synchronizing movements of saidsensor means and said surface modifying means, and control means forcontrolling the relative elevational changes produced in each of saiddiscrete areas by said surface modifying means in response to theposition of said sensor means with respect to each of said plurality ofguides.
 12. Optical surface generating apparatus according to claim 11wherein each of said guides retains information regarding apredetermined range of elevational error relative to a referenceelevation, and wherein said sensor means sequentially moves relative tosaid plurality of guides from the guide retaining information of largestelevational error relative to said reference to the guide retaininginformation of least elevational error relative to said reference. 13.Optical surface generating apparatus according to claim 12 wherein saidguides comprise a plurality of contour maps, the contour lines of eachmap representing points of constant elevational error relative to saidreference.
 14. Optical surface generating apparatus according to claim13 wherein each of said plurality of contour maps have the areas betweendifferent contour lines sensitized for the production of activating ordeactivating surface modifying action by said surface modifying means inresponse to passage of said sensor means over said sensitized portions.